1. Field of the Invention
The present invention relates to a novel skin moisturizing composition and application thereof. Particularly, the present invention relates to an anhydrous composition of small-molecule polysaccharides and application thereof.
2. The Prior Art
Skin functions as the first barrier against the external damages from the environment, such as UV radiation, pathogens, friction. From outside to the inside, skin contains the layer of epidermis, which consists of sebum, the horny layer, the granular layer, and the basal layer, the layer of dermis, which primarily consists of the connective tissue, and the hypodermis. With age, skin shows signs of aging, including wrinkles, fine lines, laxity, and sunken cheeks. The development of these signs of aging on skin results from many factors, for example, a lack of hyaluronic acid (abbreviated as HA), and deficiency in collagen. Among these factors, a lack of HA causes a decrease in skin hydration level, and leads to a decrease in skin plumpness and elasticity.
Hyaluronic acid, also termed hyaluronan or hyaluronate, is an essential component of the cellular matrix. HA in skin is mainly localized to the dermis and is able to retain water. This characteristic of water retainment comes from the ability of HA to hold high levels of water, which is up to 1000 ml water for 1 g of HA. HA is a polymer of disaccharides, with the disaccharide unit being glucuronic acid and acetyl-glucosamine. In a human body, the molecular weight of a hyaluronic acid molecule is about 5 kDa to 10 MDa.
To resolve the aforementioned issues of a lack of HA and decreased skin hydration level with age, a variety of products for moisturizing skin have been sold in the market, most of which are hydrous products containing high molecular weight HA with a molecular weight of millions of Dalton. Topical administration of these products onto the skin may increase moisture of the skin surface and prevent water loss from the skin towards the environment, an effect called barrier for moisture-lock. Recently, skin care products manufacturers have also developed hydrous products for moisturization containing small-molecule HA, with a molecular weight from 10 kDa to lower than 1 MDa, to enhance skin absorption of HA and thus to promote the ability of skin to retain water. However, this attempt is of little success.
The limited moisturizing effect of the marketed products containing small-molecule HA may be due to two reasons. First is the inferior quality of small-molecule HA. The second reason is the formulations of the moisturizing products containing small-molecule HA. The methods for industrial preparation of small-molecule HA are mostly chemical degradation, which breaks high molecular weight HA into small-molecule HA by acid degradation, alkaline degradation, or oxidative degradation. This preparation is simple, but the molecular size of the resulting small-molecule HA is usually irregular or the molecular structure is destroyed, leading to a lowered effective concentration of the small-molecule HA capable of penetrating the gap (about 40-50 nm) between keratinocytes in the horny layer of skin, or less water absorption by the small-molecule HA. These in turn affect the effect of the moisturizing products containing small-molecule HA.
Regarding the formulations of the moisturizing products containing small-molecule HA, because all marketed HA products for moisturization contain water, and the swelling property of HA causes enlargement in the size of the small-molecule HA, this enlarged size in turn hinders the penetration of the small-molecule HA across the horny layer of skin.
Therefore, there is a need to develop a novel anhydrous composition comprising small-molecule HA of regular size and structural integrity, allowing its effective penetration across the horny layer of skin and effectively increasing skin hydration level. Furthermore, other polysaccharides that absorb and retain water may be used in this novel formulation of the anhydrous composition for development of novel skin moisturizing products.